function ChangDate(formyear,formmonth,formday,isBlank){
	var i;
	var j;
	var year,month,day;
	year=formyear.value;
	month=formmonth.value;
	if (month=="2"){
		if (((year%400)==0) || (((year%100)!=0) && ((year%4)==0))){
			j=29;
		}else{
			j=28;
		}
	}else{
		if (month=="4" || month=="6" || month=="9" || month=="11"){
			j=30;
		}else{
			j=31;
		}
	}
	var k=formday.length;
	for (i=0;i<k;i++){
		formday.remove(formday.i);
	}
	if (isBlank){
		var oOption = document.createElement("OPTION");
		oOption.text="請選擇";
		oOption.value="";
		formday.add(oOption);
	}
	for (i=0;i<j;i++){
		var oOption = document.createElement("OPTION");
		oOption.text=i+1;
		oOption.value=i+1;
		formday.add(oOption);
	}
}